This invention concerns a vibration damped hand held rotary grinding machine, in particular a grinding machine of the above described type comprising a housing, a rotation motor, an output shaft drivingly coupled to the motor and having mounting means for attachment of a grinding wheel, two handles rigidly mounted on said housing and extending in substantially right angles relative to said output shaft as well as to each other, and a sector-shaped nonresilient safe guard which is rigidly attached to the housing and surrounding partially the grinding wheel and which has an arc-shaped rim portion encircling partially the grinding wheel circumference.
Vibrations developed in portable grinding machines of the above type emanate from the grinding wheel and are caused by an untrue or unbalanced running of the grinding wheel. This is due to a poor balancing of the grinding wheel at manufacturing, an inaccurate mounting on the tool shaft and to an uneven wear of the grinding wheel after some times use. Vibration forces are also generated at the contact between the grinding wheel and the work piece.
Accordingly, all vibration forces developed in the machine and to which the operator is exposed via the machine housing handles emanate from the grinding wheel and are transferred to the machine housing via the output shaft. Even if an accurate preuse balancing and centering of the grinding wheel were obtained there would still be vibration forces developed during grinding, which means that measures have to be taken to minimize the vibration forces transferred to the operator. There are two ways for lowering the vibration force transfer to the operator, namely:
(a) insulating the handles by resilient vibration absorbing means, and
(b) employing means for absorbing the vibration forces, and, thereby, damping the vibrations in the machine housing.
Whereas a large variety of resilient vibration insulating handles for portable power tools have been used in the past, there are no examples in prior art of any effective vibration mitigating or damping means or of any measures taken to reduce substantially the vibrations in the machine housing.
The object of the invention is to accomplish an improved vibration damped hand held rotary grinding machine in which the vibration forces transferred to the machine housing via the output shaft are effectively counteracted and absorbed. This is obtained by changing the inertia characteristics of the machine.
Preferred embodiments of the invention are hereinafter described in detail with reference to the accompanying drawings.